In a number of industries, it is highly desirable to determine and map the out-of-plane displacements of structural elements during loading. In the aircraft industry it is traditional to predict buckling failures in composite structures by employing empirical techniques. Predictions have been based on finite element analysis and a large number of failing load tests performed on stiffened shear panels, compression panels, and beams in universal test machines. The tests have provided very little information on the deformation of the structures as a function of applied load magnitude Analysts and designers have had virtually no test correlation of any parameter except failing load. The Moire method has been employed to map surface contours and therefore is applicable to investigating the problem of buckling of stiffened composite elements. More particularly, the Moire method has been utilized to determine out-of-plane displacements, the initiation of buckling, and the number and shape of the buckling nodes. The advantage of the Moire method is the ability of an investigator to create a full field contour map of the surface being viewed.
In the past the grilles necessary to create Moire fringes have been traditionally fabricated from optically flat plates having precisely etched lines formed therein. This involves substantial expense